What do you have, and what kind of cake? Shortening, oil (decrease liquid in recipe), applesauce or another fruit puree...

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Amelia, married to Bear since 12/31/04; our daughter Rowan was born 8/6/09; our daughter Sapphira was born 8/17/12; due with DD3 6/17/15 (but after one two weeks late and one three weeks early, I'm not expecting a due-date baby!)

i have subbed in oil for butter and vice versa many times. the recipe just needs a fat of some kind. coconut or olive oil is my go-to, but i would think vegetable oil would work too, it's the same concept. i usually just do a 1 to 1 and don't mess much with other ingredients. with something like a cake recipe, i think you'll be ok, even if you don't decrease other liquids or anything. if you feel like it's too runny, just add a little extra flour after you mix it